This invention relates to means for sharpening microtome blades, which blades are normally used for obtaining tissue or other sections for laboratory examination.
Microtome blades consist of a wedge of steel, tungsten carbide or other hard material normally having a maximum thickness of 11/2 inches which taper to a sharp edge. The blades may normally have a width of up to 21/2 inches and a length of up to 20 inches.
Conventional sharpening techniques normally consisted of lapping each side of the wedge on a rotating or reciprocating rigid plate of hard material which was charged with a suitable lapping compound. Because of the need to obtain a fine edge very fine particle size abrasives were necessary and because of this the cutting action during sharpening was very slow. In fact where a blade had suffered severe damage the lapping time could be up to 8 hours. Also because the lapping consisted of two hard bodies in contact the cutting was dependent on the angle of the blade relative to the plate and also to the pressure. It was found that the angle or pressure were incorrect there was a tendency for a burr to form on the edge of the blade which burr was most desirable when the blade was in use. Also because of wear in the lapping plate and the sensitivity of the blade to location it was difficult to get repeatable performances in sharpening.
In order to overcome or minimize these difficulties the machine described in our Australian Patent No. 400,050 was developed. This machine has two sets of opposed meshing and spaced discs of which one set is a honing or grinding set and the other set is a polishing set. In use of this machine the blade to be sharpened was traversed across the point of intersection of the honing discs to partly resharpen the blade and then the required final finish was obtained by moving the blade along the point of intersection of the polishing discs. The sharpening process and apparatus of our previous invention was such as to allow a major percentage of the material to be removed to be removed by the grinding discs whereby speeding the sharpening process substantially.
This was substantial improvement on the previously proposed arrangement but still suffered from a disadvantage in that any mismatching between the location of the discs could affect the edge finally obtained on the blade.